1. Field of the Invention
The present invention relates to a gas injector for injecting gaseous fuel with the aid of a dual valve needle.
2. Description of the Related Art
Apart from liquid fuels, gaseous fuels, such as natural gas or hydrogen, have lately also been used for operating vehicles to an increasing extent. However, the known injectors are only conditionally suitable for these gaseous fuels, since gaseous fuels have different energy densities and volumes than liquid fuels. To ensure that internal combustion engines operated on the basis of such fuels have no excessive consumption and expel only a minimum of pollutants, it is necessary to inject the most exact gas quantities possible during each injection process. One or more injection process(es) per combustion cycle must also be possible in this context. Apart from the necessity of injecting a certain maximum quantity within a predefined period of time, there must also be the possibility of metering defined minimal gas quantities in a precise manner. A low system pressure should prevail during the process, so that a content of a gas tank can be utilized to the fullest extent possible. Furthermore, between the injection processes, the injector has to seal the gas from the combustion chamber. FIG. 1 schematically illustrates an example of the nozzle-side end of a known gas injector 1, in which an outwardly opening valve needle 3 sits on a valve seat 2 in a housing 5. FIG. 1 shows the closed state of the injector. When this injector is opened, an effective overall opening cross-section initially becomes linearly larger across the lift, as long as a released annular cross-sectional area at the valve needle constitutes the smallest cross-section. As soon as the annular gap between valve needle 3 having radius R1 and housing 5 has a smaller cross-sectional area than the cross-sectional area between valve seat 2 and housing 5 released by the lift, a blow-in injection rate is constant.
When configuring gas injectors, there is a conflict in objectives between the necessary mass flow rate during an injection and the need for the lowest possible system pressure of the gas. As a result, gas injectors must have the greatest possible flow cross-sections. However, because space is usually limited, the large flow cross-sections are frequently unable to be realized by simple upscaling of the dimensions of the injectors, especially in the case of outwardly opening injectors.